This invention relates to manhole sealing systems and, in particular, to an apparatus and method for molding a sealing material to establish a fluid-tight seal and bond either between a manhole and a manhole frame supported on the manhole (or between two sections of a manhole). More particularly, this invention relates to an apparatus and method for providing a mold that can be filled with sealing material to establish a barrier seal on top of a manhole to block unwanted inflow of groundwater into the manhole through a space between the manhole and manhole frame (or between two sections of a manhole).
A manhole is a large diameter vertical pipe often made of brick or a series of precast concrete sections that extends downward from a point just below street level to a buried sewer pipe included in a municipal sewerage system. Typically, a heavy cast iron manhole frame is placed on the circular top edge of the manhole to hold a manhole cover above the top end of the manhole at street level. While the manhole cover is visible to someone standing on the street, the manhole frame supporting the cover usually is hidden mostly from view by the surrounding street or sidewalk as long as the manhole cover is in place to block access into the manhole.
In some cases, the street or sidewalk pavement around the manhole frame acts to hold the manhole frame in place on the manhole. It is also known to use bolts or other hardware to anchor the manhole frame to the underlying manhole. The familiar manhole cover rests on a circular ledge provided near the top end of the manhole frame to lie at street level. Removal of the manhole cover from the frame exposes a vertical access aperture that extends downwardly through the hollow manhole frame to enable service workers to pass through the manhole frame to reach the downwardly extending manway passage provided inside the manhole.
Unwanted leakage or "inflow" of fluids such as rainwater or groundwater into a manhole connected to a sewage disposal sewer system is a serious problem. The typical sewage treatment plant provided to process sewage conducted through a sewage disposal system is designed to handle sewage only and is not designed to have enough capacity to handle large volumes of surface water that leak into the sewage disposal sewers through leaky manholes. Typically, each municipality will include two separate sewerage systems. One system of sewers is provided to carry off sewage and other refuse liquids and waste products to a sewage treatment plant. The other system is often referred to as the "storm sewer" system and is connected to street drains and the like to carry off surface water.
A small or large gap between the top face of the manhole and the bottom face of the manhole frame (or at the joint between two abutting manhole sections) can provide just enough space for significant amounts of rainwater, groundwater, or other liquids to leak from the surrounding ground into the manhole and the sewage disposal sewer pipes connected to the manhole. Manhole leakage problems can cause too much surface water or other fluids to be introduced into the sewage disposal sewer system at one time and therefore overload the capacity of various sewage treatment stations included in the sewerage system. The capacity of a sewerage system having a sizable number of leaky manhole frames can be overloaded quite easily during prolonged and heavy rainstorms.
A gap between a manhole frame and an underlying manhole large enough to permit surface water to leak into a manhole can develop in several different ways. Manhole frames tend to vibrate due to loads applied by traffic moving on the street and over the manhole cover and, over time, such vibration can cause even heavy manhole frame to move off the underlying manhole to form a gap therebetween. Such movement can occur even though the manhole frame is initially anchored in some way to the manhole. Also, any seal established between the manhole and manhole frame can deteriorate or fail over time and cause a leakage gap to develop.
A leakage gap can also develop at the joint between two abutting manhole cylinders. Manholes are typically formed by connecting precast concrete cylinders together in series to establish a long manhole unit. Water inflow problems can also arise if any leakage occurs at the joint between a pair of adjoining cylinders. Poor anchoring and sealing connection problems are not limited only to manhole frame/manhole connections. It is also common for leaks to develop because one manhole cylinder has moved relative to an adjoining manhole cylinder or because a seal provided between the two cylinders has failed.
An apparatus and method for molding a sealing material to establish a fluid-tight sealing bond closing any gap between an inground manhole and a manhole frame without removing the manhole frame from its mounted position on the manhole would simplify rehabilitation of leaky manholes. An apparatus and method that could also be used to fill and close any gap at the joint between abutting manhole cylinder portions would also provide many benefits to manhole installation and rehabilitation work crews. Also, an apparatus and method that could be applied to solve fluid inflow problems affecting a great number of manholes in a sewerage network quickly, at low cost, and without making it necessary for service workers to carry a lot of extra tools would be welcomed by many managers of city and metropolitan sewerage systems.
According to the present invention, an innovative method is provided for providing a sealed bond between a manhole having an annular top face and a manhole frame configured to mount on the annular top face of the manhole. The method can also be used to provide a sealed bond between two adjacent manhole sections. The method includes the steps of establishing an annular channel on the annular top face of the manhole and filling the annular channel with a liquid sealing material. The method further includes the steps of putting the manhole frame (or other manhole section) over the annular top face of the manhole and in contact with the liquid sealing material in the channel and then curing the liquid sealing material. Once cured, the liquid sealing material bonds the manhole to the manhole frame (or other manhole section) and establishes a fluid-tight seal therebetween to block inflow of fluid into the manhole through a space between the manhole and the manhole frame (or other manhole section).
In preferred embodiments, the annular channel is established on top of the manhole by placing an inside channel ring on the annular top face of the manhole adjacent to an interior side wall of the manhole and placing an outside channel ring on the annular top face of the manhole adjacent to the exterior side wall of the manhole. The inner diameter of the outside channel ring is greater than the inner diameter of the inside channel ring so that the two channel rings can be arranged on top of the manhole to establish the annular channel therebetween. It is preferable to use an adhesive material to hold the inside and outside channel rings in place on the annular top face of the manhole during the filling, putting, and curing steps.
It is desirable to prepare the surface of the annular top face of the manhole prior to placing the inside and outside channel rings thereon to promote bonding of the manhole to the liquid sealing material contained in the annular channel upon curing of the liquid sealing material. Likewise, it is desirable to prepare the surface of the annular bottom face of the manhole frame (or other manhole section) prior to placing the manhole frame on top of the channel rings to promote bonding of the manhole frame to the liquid sealing material contained in the annular channel upon curing of the liquid sealing material. The liquid sealing material is preferably either polyurethane encapsulate (such as ENCAPSEAL), epoxy, or fiberglass that is formulated to cure after a predetermined period of time to establish a water-tight pliable seal blocking inflow of water into the manhole through the space between the manhole and the manhole frame (or other manhole section) and bonding the manhole to the manhole frame (or other manhole section).
Advantageously, the method in accordance with the present invention can be used to bond a manhole frame (or other manhole section) to a manhole in such a way as to block inflow or leakage of fluid into the manhole. A novel manhole seal molding kit is provided to enable workers to practice the inventive method in the field easily and at low cost. The kit has component parts such as the inside and outside channel rings which are capable of being assembled in the field at a manhole to provide a mold for containing a liquid sealing and bonding material in a walled reservoir in contact with a manhole frame (or other manhole section) and an underlying manhole.
Once the two channel rings are properly positioned and retained on the manhole, liquid sealing material can be deposited in the annular channel formed by the coaxially aligned channel rings. The heavy manhole frame (or other manhole section) can then be lowered onto the top portion of the channel rings to lie in contact with the pool of liquid sealing material retained in the annular channel. Once the sealing material hardens or cures in the annular channel mold, a fluid-tight seal is established to block or plug any gap between the manhole frame (or other manhole section) and the manhole, and the manhole frame (or other manhole section) is bonded to the manhole to anchor the manhole frame (or other manhole section).
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.